Core constructions for variable inductors and parametric devices

ABSTRACT

Various core constructions are disclosed for use with variable inductors and parametric devices, the cores having supplemental core pieces acting in some cases as magnetic shunts and in other cases as return paths, or both, for the input and/or output portions of a magnetic core such as that disclosed in U.S. Pat. No. 3,403,323.

[ Mar. 7, 1972 United States Patent I Wanlass [56] References Cited UNITED STATES PATENTS 2,916,714 12/1959 [54] CORE CONSTRUCTIONS FOR VARIABLE INDUCTORS AND PARAMETRIC DEVICES .....336/2l2 X 336/155 X ....323/56 Donavy......................... [72] inventor: Craven: L. Waniass, 9871 Overhill Drive, 3 13 5 9 5 King, at

Santa Calif- 92705 3,403,323 9/1968 Wanlass.....,.......... Aug. 31, 1970 [22] Filed:

Primary Examiner-Thomas J. Kozma Attorney-Howson and Howson [21] Appl. No.: 68,130

ABSTRACT Various core constructions are disclosed for use with variable inductors and parametric devices, the coreshaving supplemental core pieces acting in some cases as magnetic shunts and in other cases as return paths, or both, for the input and/or output portions of a magnetic core such as that disclosed in U.S. Pat. No. 3,403,323.

[52] U.S. CL..............................336/l60, 336/165, 336/212, 336/215 [51] Int. [58] Field of Search............ .....336/155, 160, 165, 212, 214, 336/215; 323/56 14 Claims, 11 Drawing Figures PATENTEDMAR 7 I972 3,648,206

SHEET U BF 4 5/ Fm. 5. 5m

7 INVENTOR. FI ceA V6/V5 4. WAN/A as M vfi ws A TTOEA/(E v5 CORE CONSTRUCTIONS FOR VARIABLE INDUCTORS AND PARAMETRIC DEVICES BACKGROUND OF THE INVENTION areas of contact or common zones. Each of the C-cores is provided with a winding, one of the winding acting as a load winding and the other winding serving as a control winding. The principles of operation of the inductor are set forth in the patent, the disclosure of which is incorporated by reference herein and need not be repeated in detail here. In application, Ser. No. 821,933, filed May 5, 1969 by Leslie Kent Wanlass, there is disclosed a parametric device which in some embodiment incorporates the variable inductor disclosed in U.S. Pat. No. 3,403,323. The principles of operation of the parametric device are disclosed in full in application, Ser. No. 821,933, the disclosure of which is incorporated by reference herein, and need not be described in detail here.

Briefly, the parametric device there disclosed operates by parametrically transferring energy from an AC source to a resonant circuit made up of a capacitor and the load or output winding of a variable inductor by periodically changing the inductance of the inductor. Magnetic flux is caused to flow in both sections of the core as a result of the currents passed through the two windings. These fluxes interact in the four common regions of the core to accomplish the inductance control function.

In practice, the cores of the variable inductors used in these parametric devices have been constructed in the conventional manner of making C-cores or have been molded from ferrite material. While the devices have been satisfactory in operation, core construction costs have been relatively high and efficiencies, particularly in those devices utilizing C-cores, have not been as high as theoretically possible. This is particularly true in those instances where either the input side or the output side of the core are driven at higher flux density levels than is required for the control function in the four common regions. In such a case, since all the flux in one of the core sections must return through the other, magnetic losses are unduly increased. This is particularly true where the less expensive grain oriented magnetic material is used in the construction of the C-cores because the flux, as it passes through its return path, is generally normal to the grain orientation of the material. Of course, if the more expensive randomly or cubic oriented magnetic material is used, this problem is substantially reduced.

In such prior devices, the input current is sometimes undesirably high due to saturation of the input magnetic core piece. In general, this is caused by the output core piece saturating and in turn causing saturation of the input core piece. When this occurs, the device presents its minimum inductance with the result that any increase in input voltage produces an increase in input current with correspondingly I R losses and increased magnetic losses.

Although it would be much cheaper to do so, stamped laminations have not been used in the construction of these inductors and parametric devices because of the cumulative airgap that would be present in the return path for each of the fluxes.

SUMMARY OF THE INVENTION According to the present invention, it has been found that the operation of such an inductor, and particularly such a parametric device, can be made more efficient by providing the core thereof with supplemental core pieces to provide shunting and/or return paths for the magnetic fluxes generated in each core section by its respective winding. In this way, it is possible in some cases to limit the flux density in the four common zones to that level which produces the desired control function. Any additional flux will complete its magnetic circuit through the supplemental core pieces or shunts. The level of the flux density in the four common zones can be established by means of an airgap in the path including the supplemental core member.

The use of such supplemental core pieces also permits the main core sections to be constructed out of stamped Cl laminations, thus greatly facilitating their manufacture and reducing their cost.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a parametric device according to the aforesaid application, Ser. No. 821,933;

FIG. 2 is a perspective view of a first embodiment of a core structure according to the present invention;

FIG. 3 is a perspective view of one-half of the core structure of FIG. 2;

FIG. 4 is a front elevation of a second embodiment of a core structure according to the present invention;

FIG. 5 is a side elevation of the core structure of FIG. 4;

FIG. 6 is a front elevation of a third embodiment of a core structure according to the present invention;

FIG. 7 is a side elevation of the core structure of FIG. 6;

FIG. 8 is a front elevation of a fourth embodiment of a core structure according to the present invention;

FIG. 9 is a side elevation of the core structure of FIG. 8;

FIG. 10 is a front elevation of a fifth embodiment of a core structure according to the present invention; and

FIG. 11 is a side elevation of the core structure of FIG. 10.

DESCRIPTION OF THE INVENTION As an aid in understanding the present invention, it is believed that a brief description of the operation of the variable inductor disclosed in U.S. Pat. No. 3,403,323 and the parametric device disclosed in application, Ser. No. 821,933 would be of help. The variable inductor comprises a magnetic core having a pair of windings thereon. The core is constructed so that it has four common regions or legs" and two end or joining portions for magnetically coupling the common regions. The coils are wound with their axes displaced at and the core is so formed that normally there is no mutual inductive coupling between them, and the flux components generated as a result of currents in the two windings are at all times in opposing relationship in two of the legs" and in additive relationship in the other two legs. As a result of this construction, the current in one of the windings, referred to as the control winding, generates a magnetic flux which controls the reluctance of the magnetic circuit encompassed by the second winding, referred to as the load winding, in such a manner that variations in the flux caused by variations in the current in the control winding caused the hysteresis loop of the magnetic circuit encompassed by the load winding to be effectively rotated thereby varying the inductance of the load winding. Because of the construction of the device, the inductance varies at twice the frequency of an alternating current applied to the control winding.

This phenomenon is utilized in the parametric device disclosed in application, Ser. No. 821,933. In that application, a capacitor is coupled to the load winding of the variable inductor to form a resonant circuit. Energy is transferred to the resonant circuit by pumping the control winding with an alternating current of the same frequency as that to which the resonant circuit is tuned, that is, the output frequency thereby varying the inductance at twice that frequency. Once the parametric circuit builds up to its stable oscillating point, reasonable variations in magnitude of the pumping source do not appreciably affect its output. Therefore, by coupling the line to be regulated to the control winding of the inductance device, a regulated, almost perfect sine wave, displaced 90 in phase with the input, can be taken from the resonant circuit. Since there is no direct transformer coupling between the windings, the device serves as a bilateral filter, removing transients and noise generated in either the line or the load.

The core structures of the present invention are particularly useful in parametric circuits of the type disclosed in the aforementioned application and in modifications and improvements thereto. For example, they are particularly useful when employed in a parametric voltage regulator with high power transfer capacity of the type disclosed in application, Ser. No. 750,914 filed Aug. 7, 1968 by Sylvan D. Wanlass, which application has been assigned to the assignee of the present application. In that application, a circuit is disclosed in which power transfer is accomplished in two modes-by parametric coupling and by flux coupling or direct coupling, or a combination of the latter two. It is there disclosed that if a tank circuit of a parametric regulator is expanded to include a winding which is flux coupled to the input winding of the device, or is directly coupled to the input, substantially greater amounts of power can be transferred through the device without any appreciable loss in the regulating characteristics of the device. This high power capacity, and the resulting high currents in the output winding, result in some of the problems for which the core structures of the present invention provide solutions.

As the invention has to this point been primarily used'in connection with such parametric circuits, it will be described in connection therewith. It should be understood, however, that such description is for the purpose of clarity and not to be considered a limitation on the usefulness of the present invention.

Turning first to FIG. 1 there is illustrated a parametric device according to the teachings of Ser. No. 821,933. As shown, the parametric device comprises first and second C cores l and 11 rotated 90' to each other and brought into open end abutment. The core section is provided with an input winding 12 while the core section 11 is provided with an output winding 13 which is coupled in a resonant circuit with a capacitor 14. Four common regions or zones 15, 16, 17 and 18 are formed where the two core sections 10 and 11 are joined together. These zones must pass all the magnetic flux generated by each of the-windings 12 and 13 as described in the aforementioned US. Pat. No. 3,403,323. It can be seen that a point can be reached, either because of high current in the output winding 13, or the input winding 12, or for other reasons, where the common regions 15, 16, 17 and 18, or some of them, become saturated, that is, an increase in control current (whether this control is exercised by the input winding on the output winding or vice versa) can have no further effect in varying theinductance which the control winding presents to the source. In other words, the winding acts as an air core inductor having a relatively low reactance with the result that very high current can be drawn, thus increasing I R loss, possibly to the point of burning out. Since the core material is saturated, the magnetic losses are also much higher than in the desired nonsaturated condition.

To illustrate, let it be assumed that the input voltage to be supplied to the input winding 12 might vary over a wide range. In the event that the input current has a magnitude sufficient to cause saturation in the common regions 15, 16, 17 and 18, the reactance presented to the source would be at a minimum, and if the voltage then increased, high surge currents would result. Similarly, if the output circuit was circulating large amounts of energy so that the currents present in the output winding 13 were large enough to saturate the common regions, large I R and magnetic losses would result in the secondary. Moreover, because the common zones would be saturated, the reactance presented by the input winding 12 to the source would be low so that large input currents would be drawn. Any of these conditions result in relatively low efficiencies and consequently higher operating costs.

These problems are solved in various ways by the different embodiments of the present invention. These embodiments have in common the technique of providing a magnetic path or paths that the flux from one or both of the windings may follow in addition to the path including the common regions. In some cases these additional paths act as shunts, that is, they provide a secondary path through which the flux in one of the core sections can close on itself without ever entering the other core section. In other cases, the additional core pieces act as return paths, that is, in some cases completing the magnetic circuit external of the core sections and permitting interaction of the fluxes without requiring the flux from one core section to enter the other core section thereby reducing the magnetic losses by not forcing the magnetic flux to go perpendicular to the core grain orientation.

Turning now to FIGS. 2 and 3 there is shown an example of a core having a shunt path associated with its input side. A core 20 is formed of a pair of mating C-core sections 21 and 22, each of which is provided with a winding 23 and 24 respectively, winding 23 being the input winding and winding 24 being the output winding. The input core 21 is provided with a shunt segment 25 which is positioned between the four areas where the cores 22 and 21 contact each other, i.e., the four common zones where flux interaction occurs. The shunt segment 25 can be of any suitable magnetic material but is preferably a further C-core section. As can best be seen in FIG. 2, at least one end of the shunt segment 25 is slightly displaced from the core 21 to leave an air gap 26. Of course, for mechanical or other reasons, this air gap may be filled with a suitable dielectric if desired.

As will be apparent, the core 20 with its associated windings 23 and 24 will operate in the normal manner disposed in US. Pat. No. 3,403,323 until a point in the operation of the device is reached where one or more of the common zones has such a high flux density that the reluctance of the path 25 to the flux generated by the input winding 23 is less than the reluctance of the path formed by the common regions and a portion of the core 22. At this point, any additional flux, for example, that was caused by a larger input current will follow the path formed by the shunt segment 25. The point at which this will occur, of course, will be determined by the width of the airgap 26. The presence of the shunt segment 25 causes the winding 23 to present a substantial reactance to the line even when the basic device is saturated."

If desired, the shunt segment 25 can be constructed out of conventional laminations. In such a case, the laminations are preferably ground and lapped so that airgap uniformity is achieved. In any event, the use of such a shunt results in better isolation between the input and output in a parametric device of the type described in application, Ser. No. 821,933 because the shunt will act to maintain a constant maximum flux density in the secondary core section 22. This will also result in better voltage regulation.

If desired, the center shunt shown in FIGS. 2 and 3 can be replaced by a pair of side shunts as shown in FIGS. 4 and 5. In these figures, a core 30 has an input section 31 and an output section 32 provided with input winding 33 and output winding 34, respectively. A pair of laminated shunts 35 and 36 are provided on the sides of input core section 31 and are separated therefrom by suitable airgaps 37 and 38 which may be filled, if desired, by a suitable dielectric material. As was the case with the center shunt, it is preferable that care be taken in grinding and lapping the laminations of the shunts 35 and 36 so that a uniform airgap is provided. Once again, the size of the airgaps 37 and 38 determines the point when a magnetic circuit in the primary core section begins to be completed through the shunts 35 and 36 instead of all of the flux returning through the secondary core section.

In many cases it is desirable to provide the core with shunting segments on the output section of the core in place of, or in addition to, the shunting segment on the input side of the core. Such a construction is shown in FIGS. 6 and 7. In these figures, a core 40 has an input section 41 and an output section 42 composed of two C-cores rotated at and joined together. The input section 41 is provided with side shunt segments 43 and 44 separated from the section 41 by appropriate air gaps. In a similar manner, the output section 42 is provided with a pair of side shunt segments 45 and 46 which are also separated from the section 42 by appropriate airgaps. Of course, if desired a shunt of the type shown in FIG. 2 could be used on the output core section. In FIG. 6, the flux generated by current in the output winding 48, as illustrated by arrows, passes through the section 42 and returns along the edge of the section 41 until a predetermined flux density is reached in the four zones common to the two core sections 41 and 42. At that point, flux also begins to complete a magnetic path through the shunts 45 and 46. In this way, the input section 41 of the core 40 is protected from fluxes which otherwise saturate it.

Similarly, in FIG. 7, the arrows show the paths taken by the flux generated by the input winding 41. As can be seen, a first return path is formed through the output section 42 and a second path is formed through the shunts 43 and 44 for the purposes noted above in connection with FIGS. 2 through 5. In some cases, it may be desirable to have the cross-sectional area of the output core section greater than that of the input core section. In such a case, it is possible to lay the shunt segments across the open end of the larger core section on either side of the smaller core section.

In some instances, the energy circulating in the output circuit is considerably greater than the energy circulating in the input circuit. This is particularly true in the case of a device such as that disclosed in the aforementioned application, Ser. No. 750,914. As pointed out in that application, a device which utilizes both flux coupling and parametric coupling can transfer significantly greater amounts of energy with the same size core than can a simple parametric device of the type described in the aforementioned application, Ser. No. 821,933. As it is presently understood, it appears that in such a high power device, the energy circulating in the output circuit is quite high with only enough energy being transferred from the input circuit to make up losses and supply the output load.

Such a circuit with a suitable shunt for the output core section as shown in FIGS. 8 and 9, the core 50 is, as in the previous figures, made up of a pair of C-cores 51 and 52 rotated at 90 to each other. Rather than being brought together, however, the sections 51 and 52 are separated by a laminated plate 53, the laminations of which are magnetically aligned with the laminations of the output core section 52, that is, flux traveling through the core section 52 can complete its path along the length of the laminations of the plate 53 rather than across the laminations. By constructing the plate 53 in this manner, it can be seen that it provides a low reluctance flux path to the flux generated in the output winding 54, but presents a very high reluctance to the flux generated by a current in the input winding 55 or the output winding 56 which is flux coupled to the input winding 55 due to the large cumulative airgap of the laminations. A capacitor 57 is connected in series with the windings 54 and 56 to form the resonant output circuit. Typically, but not necessarily, the output winding 54 which is parametrically coupled to the input winding 55 has substantially more turns than the output winding 56.

As will readily be apparent, a number of laminations may be deleted from the central portion of the plate 53, if such is desired, to increase the airgap presented to the flux in the input core section 51. However, when these central laminations are present, they can act as a shunt for the output flux in the same manner as described above. As will also be apparent, a second laminated plate could be inserted between the output core 52 and the laminated plate 53, the laminations of this additional plate running perpendicular to those of the plate 53 and thereby providing a low reluctance return path to the flux present in the input core section 51 and a high reluctance return path to the flux in the output core section 52. In such a construction, the laminated plates could serve as return paths rather than simply as shunts, and the four common zones would be at the four corners of the interface of these plates rather than in the main core sections themselves. No difference in the basic operation of the device results from the use of such plates.

By the use of such low reluctance return paths a device can be constructed of stamped C-laminations rather than from the more expensive C-cores or molded ferrites. Since all of the flux generated in one of the core sections can be returned through such an auxiliary core segment, it is not necessary for the flux to enter into the other core section at all, with the result that it is unimportant that the laminations of the other core section are arranged transversely to the path that the magnetic flux would take in the normal device.

Such a construction is shown in FIGS. 10 and 11. In these figures, a core 70 is provided with an input core section 71 and an output core section 72 both of which are constructed of stamped-C-laminations. The input core section is provided with an input winding 73 while the output core section 72 is provided with an output winding 74 coupled to a capacitor 75. Attached to the input core section 71 in any suitable fashion are a pair of bars 76 and 77 which, for example, by a suitable adhesive, may be constructed of stamped I-laminations arranged perpendicularly to the laminations making up the input core section 71. In a similar manner, a pair of bars 78 and 79 coextensive with the legs of the core section 72 are attached thereto in any suitable fashion. The laminations of the bars 78 and 79 are arranged perpendicularly to the laminations of the section 72. As can be seen from FIG. 10, a flux generated by a current in the winding 73 passes through one leg of the core section 71, through the bar 77 and then back along the laminations of the bars 78 and 79, through the bar 76 and back into the other leg of the input core section 71.

In a similar manner, as shown in FIG. 11, the flux in the output core section 72 finds its return path through the bars 76 and 77. As can be seen, the four common zones in which the necessary flux interaction takes place are no longer present at the faces of the input and output core sections 71 and 72, but rather at the four areas where the laminated bars 76-79 engage each other. This, however, does not alter the operation of the device. The use of the laminated bars asretum paths, however, does permit the use of stamped laminations in the construction of the core section 71 and 72 and thus substantially reduces their cost. If desired, the bars 76 and 77 and the bars 78 and 79 could be replaced by laminated plates such as that shown in FIGS. 8 and 9. Such plates would then serve both as return paths and as shunts and thus pennit the accomplishment of all of the advantages of the present invention.

Iclaim:

1. A variable inductor comprising:

first and second magnetic core sections, each of said core sections having an upper portion and first and second legs depending therefrom so that said core sections are generally C-shaped, said core sections being rotated to each other to form four common zones defined respectively by separate areas of each of the first and second legs of the first core section opposed to separate areas of each of the first and second legs of the second core section;

a first winding wound on said first core section between the depending legs thereof;

a second winding wound on said second core section between the depending legs thereof; and

a magnetic shunt mounted on one of said core sections joining the depending legs thereof, said shunt having an airgap therein.

2. The inductor of claim 1 wherein said magnetic shunt joining the legs of said one core section is positioned between the legs of the other core section.

3. The inductor of claim 1 wherein said magnetic shunt is positioned across one of the ends of said one core sections.

4. The inductor of claim 1 wherein a second magnetic shunt is mounted on the other of said core sections joining the depending legs thereof, said second magnetic shunt having an airgap therein.

5. The inductor of claim 4 wherein said second magnetic shunt is positioned across one of the ends of said other core section.

6. A variable inductor comprising:

first and second magnetic core sections, each of said core sections having anupper portion and first and second legs depending therefrom so that said core sections are generally C-shaped, said core sections being rotated 90 to each other to form four common zones defined respectively by separate areas of each of the first and second legs of the first core section opposed to separate areas of each of the first and second legs of the second core section;

a first winding wound on said first core section between the depending legs thereof;

a second winding wound on said second core section between the depending legs thereof; and

plate means of laminated magnetic material positioned between and engaging the depending legs of said core sections, the laminations of said plate means being parallel so as to prevent a low reluctance path to flux generated-in one of said core sections as a result of current in the winding thereof and a high reluctance path to flux generated in the other of said core sections as a result of current in the winding thereof.

7. The inductor of claim 6 wherein said plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said other of said core sections.

8. The inductor of claim 6 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said other core.

9. The inductor of claim 6 wherein second plate means of laminated magnetic material is positioned between said plate means and said one core section, the laminations of said second plate means being parallel to each other but substantially perpendicular to the laminations of said first plate means so as to present a high reluctance path to said flux generated in said other core section.

10. The inductor of claim 9 wherein said second plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said one core section.

11. The inductor of claim 9 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said one core.

12. The inductor of claim 10 wherein said plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said other of said core sections.

13. The inductor of claim 11 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said other core.

14. The inductor of claim 13 wherein each of said first and second core sections comprises a plurality of stamped C- laminations. 

1. A variable inductor comprising: first and second magnetic core sections, each of said core sections having an upper portion and first and second legs depending therefrom so that said core sections are generally Cshaped, said core sections being rotated 90* to each other to form four common zones defined respectively by separate areas of each of the first and second legs of the first core section opposed to separate areas of each of the first and second legs of the second core section; a first winding wound on said first core section between the depending legs thereof; a second winding wound on said second core section between the depending legs thereof; and a magnetic shunt mounted on one of said core sections joining the depending legs thereof, said shunt having an airgap therein.
 2. The inductor of claim 1 wherein said magnetic shunt joining the legs of said one core section is positioned between the legs of the other core section.
 3. The inductor of claim 1 wherein said magnetic shunt is positioned across one of the ends of said one core sections.
 4. The inductor of claim 1 wherein a second magnetic shunt is mounted on the other of said core sections joining the depending legs thereof, said second magnetic shunt having an airgap therein.
 5. The inductor of claim 4 wherein said second magnetic shunt is positioned across one of the ends of said other core section.
 6. A variable inductor comprising: first and second magnetic core sections, each of said core sections having an upper portion and first and second legs depending therefrom so that said core sections are generally C-shaped, said core sections being rotated 90* to each other to form four common zones defined respectively by separate areas of each of the first and second legs of the first core section opposed to separate areas of each of the first and second legs of the second core section; a first winding wound on said first core section between the depending legs thereof; a second winding wound on said second core section between the depending legs thereof; and plate means of laminated magnetic material positioned between and engaging the depending legs of said core sections, the laminations of said plate means being parallel so as to prevent a low reluctance path to flux generated in one of said core sections as a result of current in the winding thereof and a high reluctance path to flux generated in the other of said core sections as a result of current in the winding thereof.
 7. The inductor of claim 6 wherein said plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said other of said core sections.
 8. The inductor of claim 6 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said other core.
 9. The inductor of claim 6 wherein second plate means of laminated magnetic material is positioned between said plate means and said one core section, the laminations of said second plate means being parallel to each other but substantially perpendicular to the laminations of said first plate means so as to present a high reluctance path to said flux generated in said other core section.
 10. The inductor of claim 9 wherein said second plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said one core section.
 11. The inductor of claim 9 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said one core.
 12. The inductor of claim 10 wherein said plate means comprises a continuous series of magnetic laminations extending from one depending leg to the other of said other of said core sections.
 13. The inductor of claim 11 wherein said plate means comprises first and second series of magnetic laminations, each of said series of laminations extending across at least a portion of one of said depending legs of said other core.
 14. The inductor of claim 13 wherein each of said first and second core sections comprises a plurality of stamped C-laminations. 